1. Field of the Invention
The present invention relates generally to the art of ceramic orthodontic appliances and more specifically, to methods for providing the ceramic material with a porous glassy coating of high mechanical strength to enhance the bonding of the ceramic material such as polycrystalline alumina and sapphire to the tooth enamel with an interlying acrylic resin material.
In orthodontic surgical procedures, orthodontic brackets are typically attached to teeth by adhesive bonding. The surface of the teeth is often acid etched so that a micro-mechanical interlock is achieved between the resin and the etched surface. Alternatively, the surface of the tooth may be provided with a crystal growth to which a resin material is bonded. There is also mechanical bond between the bracket base abutting the tooth and the resin. This mechanical bond normally represents the weak point of the assembly and brackets can become detached from the teeth by failure of the mechanical bond of the bracket resin interface if the shear strength thereof is exceeded. More recently, there has been a substantial interest developed in ceramic orthodontic appliances because of the inherent wear resistance of ceramic materials. In addition, certain ceramic materials show substantial promise for use in more cosmetic dental appliances wherein the dental brackets may be made far less obvious by using transparent or translucent ceramic materials therefor. In particular, it has been found that polycrystalline alumina and sapphire can be used to create extremely wear-resistant orthodontic bracket appliances which also have superior cosmetic appearance and which may therefore have a profound effect on the orthodontic industry by making the wearing of orthodontic appliances more amenable to the appearance concerns of adults and older teenagers. Unfortunately, the aforementioned bonding problem of prior art orthodontic materials is even more severe in regard to ceramic orthodontic appliances because such ceramic materials inherently have extremely hard surfaces which are more resistant to adherence to bonding materials.
2. Prior Art
Although there are numerous prior art references relating to the bonding of orthodontic appliances to the surface of teeth, the prior art with respect to the bonding of ceramic materials for this purpose is quite limited because of the relatively recent consideration of ceramic materials for orthodontic applications.
U.S. Pat. No. 3,895,445 to Silverman et al is directed to adhesive compositions for orthodontic applications and specifically includes a thermosetting resin composition which adheres to tooth enamel. The resin composition is etched using a methacrylic acid ester mixture to penetrate the thermosetting resin composition and allow increased adherence to the orthodontic appliances.
U.S. Pat. No. 3,955,282 to McNall is directed to a method of mounting orthodontic brackets to teeth. In this reference the tooth is etched by phosphoric acid and a pre-mixed dental adhesive attaches the orthodontic brackets to the teeth.
U.S. Pat. No. 4,180,911 to Bullock is directed to a method for direct bonding of orthodontic structures to teeth using a fluoride pre-treatment. The tooth is etched by acid and a solution of stannous fluoride is applied to the dried tooth surface to protect from the development of caries and also act as a bridging means between the tooth surface and the adhesive to enhance the bond strength.
U.S. Pat. No. 4,010,545 to Kilian et al is directed to adhesive bonding of orthodontic brackets to teeth. The tooth surface is acid etched, rinsed and dried. A thixotropic activated monomer is applied to the surface of the tooth or to the orthodontic bracket. The thixotropic activated monomer is activated prior to the application.
U.S. Pat. No. 3,625,916 to Newman is directed to a synthetic plastic dental adhesive. This reference is relevant because it relates to the use of silica and a filler selected from the group consisting of silica gel and pulverulent, fused quartz glass.
U.S. Pat. No. 4,068,379 to Miller et al discloses an orthodontic appliance with a porous tooth-abutting face. The appliance is bonded directly to a tooth utilizing a composite base with a porous tooth-abutting face. The base is formed by rolling a mesh in strip form to form flats on at least one surface of the mesh which is to be in contact with a solid base portion and then bonding the mesh to the base.
Canadian Patent No. 1,187,727 to Smith et al relates to the use of a particular coating applied to dental attachments on the tooth engaging surface thereof which coating enables improved bonding between the tooth and the dental attachment. Methods such as fusion or sintering may be used to apply the particular coating to the attachment. The coating may take the form of discrete particles spaced apart from each other on the surface of the form of a layer or multiple layers of particles bonded together to produce a network of interconnected pores.
Unfortunately, none of the prior art known to the applicant herein specifically addresses the problems associated with bonding an extremely hard ceramic material orthodontic bracket to the surface of a tooth. Accordingly, none of the prior art known to the applicant teaches or even suggests the particular solution of the present invention.